DESCRIPTION: (Taken from Abstract) Cell-associated HIV variants are associated with enhanced sexual transmission, yet the role of cell- associated HIV on transvaginal infection is poorly characterized. While cell-associated SIV is not efficiently transferred (if at all) across the vaginal mucosa, feline immunodeficiency virus (FIV) mimics the cell-associated versus cell-free diversity apparent in HIV vaginal transmission. We propose to use FIV infection to study vaginal transmission of cell-associated lentivirus and address questions difficult to resolve in HIV infected people. Increased cellularity in semen correlates with an increased rate of HIV vaginal transmission but the cells responsible for transvaginal lentivirus infection and the role in pathogenesis remain unknown. Experimental vaginal transmission of FIV suggests that, at minimum, both T cells and macrophages are important in lentivirus transmission. Aim 1 will use fluorescent labeled, FIV-infected PBMC to identify the cells responsible for transvaginal FIV infection. The relative efficiency of vaginal transmission by lymphocytes and macrophages will be determined by vaginal inoculation of serially diluted FACS sorted cell populations. HIV infected lymphocytes can rapidly and efficiently infect the apical surface of mucosal epithelial cells in culture, thus creating a different pathway for viral pathogenesis and immune induction. Tissue reservoirs of virus are more extensive following mucosal transmission of cell-associated FIV than with cell-free FIV providing an animal model correlate to the in vitro HIV findings. Aim 2 will determine whether the early pathogenesis of cell- associated vaginal transmission is altered by unique targets (e.g. vaginal epithelium) or immunologic selection. Protection against sexually transmitted HIV will require protection against cell-associated HIV as well as cell-free HIV. Parenteral SIV immunization studies suggest that the vaccine induced immunity needed to protect against cell-free vaginal challenge will be insufficient to protect against cell-associated challenge. Strong cell-mediated responses at the mucosa and associated lymphoid tissue are likely necessary to resist cell-associated vaginal challenge. Aim 3 tests the ability of a lymphoid targeting vector (venezuelan equine encephalitis replicon particles) to induce FIV- specific vaginal immunity. FIV expressing replicon particles will be used to identify the optimal route of immunization to induce strong cell-mediated immunity in the vaginal mucosa. Vaginal challenge with cell-associated FIV will test the correlates of protection.